This invention relates to devices for continuous pitch variation of stringed instruments, especially electric guitars and electric basses, such as described in my U.S. Pat. Nos. 4,044,645 and 4,137,812, and in the German Pat. No. P 15 97 028 and furthermore in the German Offenlegungsschriften (published specifications) OS-26 35 905.7 and OS-27 04 636.2.
In such devices the neck of the instrument is extended by an extension piece and is movably mounted on the body of the instrument. The movability of the neck renders possible a control of a continuous change of the tension of the strings and with that a continuous variation of the pitch. Through the use of a locking-device, the neck can be made movable or immovable, just as it is necessary when playing.
It has turned out in practice that the locking-device is of great importance for a good operation and satisfactory use of the whole device to render possible a masterly playing. For normal use it is necessary that the opening or unlocking and the locking can be controlled and executed in a fast and exact operating manner. A faultless manipulation of the locking-device must be guaranteed in both playing postures, that is, with the player either standing or sitting.
The arrangement of a lever-plate as shown in U.S. Pat. No. 4,137,812 (see part 41 in FIG. 4) has disadvantages when sitting, but especially when standing, caused through the fact that an unintentional operation may easily be produced, when the instrument is held against the body of the player with the usual pressure.
An object of the invention is to eliminate said disadvantages and to render possible a fast and exact control and operating of the unlocking and locking of the neck. Another object of the invention is an improvement of the tension spring which carries the tension of the strings.